Aditya R. Gusman, Yuichiro Tanioka, T Kobayashi, Hamzah Latief, Wahyu Pandoe
Joint inversion study using tsunami waveforms and InSAR data provides a new way to understand the magnitude and spatial extent of subduction zone earthquakes. A great earthquake (Mw 8.5) occurred on 12 September 2007 off the west coast of Bengkulu, Indonesia. The tsunami generated by the event was recorded by tide gauge stations around the Indian Ocean and by two bottom-pressure sensors in the deep sea. The ground surface displacements produced by the earthquake on Pagai Islands and on Sumatra Island were observed by Interferometric Synthetic Aperture Radar (InSAR). We estimated the slip distribution of the earthquake by joint inversion incorporating a spatial smoothness constraint, using tsunami waveforms and InSAR data. The total released seismic moment calculated from the slip distribution is 6.7 × 1021 N m (Mw 8.5), consistent with the seismic moment of the Global CMT solution, 6.71 × 1021 N m. The maximum observed tsunami heights along the coast of Bengkulu agree with those computed from the slip distribution. The slip amount of the 2007 earthquake is smaller than the amount of potential slip that has been accumulated since after the 1797 and 1833 events. The premise is that, averaged over long periods of time, the entire fault must slip equal amounts. Therefore the 2007 great earthquake could be followed by several great earthquakes that will rupture the plate interface until the potential slip that has been accumulated is completely released.